A study of the effect of ozone and antioxidants on ozone-sensitive loblolly pine

Abstract

Ozone, a phytotoxic air pollutant, is formed from photochemical reactions of hydrocarbons and nitrogen oxides in the troposphere. Ozone is taken into the plant through the stomata, and quickly broken down into hydroxyl radicals. These hydroxyl radicals can oxidize portions of the cell and cause damage or may be neutralized by antioxidants. Ozone is known to have a variety of negative effects on plants, including reductions in growth, changes in membrane permeability, and increases in dark respiration. Ozone can also affect photosynthetic parameters, including decreasing photosynthesis, decreasing chlorophyll concentration, and decreasing Rubisco (ribulose1,5-bisphosphate carboxylase/oxygenase) concentration and activity. Damage from ozone might be decreased if the natural antioxidant systems of the plant could enhanced, Ozone and two antioxidants, ethylenediurea and Ozoban, were studied in loblolly pine seedlings to determine their impact on total soluble protein, Rubisco activity, and Rubisco concentration. The objective of this study was to determine how ozone and these antioxidants affect the photosynthetic enzyme, Rubisco, in loblolly pine. Seedlings were exposed to ozone ranging from charcoal-filtered air to 2.5X the ambient ozone concentration in open-top chambers at the study site. Antioxidants were applied every two weeks at the rate of 0 ppm, 150 ppm, and 300 ppm for ethylenediurea; and 0 ppm, 1030 ppm, and 2060 ppm for Ozoban. Total soluble protein was positively affected by the highest concentration of ethylenediurea and all Ozoban concentrations after the ozone peak in May. All significant negative trends in Rubisco activity due to treatments occurred in June, after the ozone peak. Treatment with 300 ppm ethylenediurea or 1030 ppm Ozoban resulted in a decrease in Rubisco activity. Late in the study, after five months of exposure, treatment with 2060 ppm Ozoban or 150 ppm ethylenediurea resulted in increased Rubisco concentrations.